The invention relates to improvements in the process of producing esterification products of aromatic dicarboxylic acids. It is known to react cyclic alkylene carbonates with aromatic dicarboxylic acids to produce bis-hydroxy-substituted esters of aromatic dicarboxylic acids as well as oligomers and polymers thereof.
U.S. Pat. No. 3,549,692 teaches the use of certain five-membered N-heterocyclic compounds containing 2 to 4 heterocyclic nitrogen atoms as catalysts in the aforementioned reaction. Also disclosed by this patent are known catalysts of the prior art including alkali metal carbonates, antimony trioxide, cerium dioxide, zinc borate, magnesium acetate and lead acetate. Other catalysts for the process are also known.
The catalysts hitherto used for accelerating the reaction have proven to be unacceptable either because of an inability to operate effectively at desired low reaction temperature, expense, subsequent contamination of resulting products, or poor selectivity in product formation.